Internet Engineering Task Force (IETF)
Request for Comments: 7851
Category: Standards Track
ISSN: 2070-1721

H. Song
X. Jiang
R. Even
Huawei
D. Bryan
ethernot.org
Y. Sun
ICT
May 2016

Peer-to-Peer (P2P) Overlay Diagnostics

Abstract

This document describes mechanisms for Peer-to-Peer (P2P) overlay diagnostics. It defines extensions to the REsource LOcation And Discovery (RELOAD) base protocol to collect diagnostic information and details the protocol specifications for these extensions. Useful diagnostic information for connection and node status monitoring is also defined. The document also describes the usage scenarios and provides examples of how these methods are used to perform diagnostics.

Status of This Memo

This is an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741.

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc7851.

Copyright Notice

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Diagnostic Scenarios  . . . . . . . . . . . . . . . . . . . .   5
   4.  Data Collection Mechanisms  . . . . . . . . . . . . . . . . .   6
     4.1.  Overview of Operations  . . . . . . . . . . . . . . . . .   6
     4.2.  "Ping-like" Behavior: Extending Ping  . . . . . . . . . .   8
       4.2.1.  RELOAD Request Extension: Ping  . . . . . . . . . . .   9
     4.3.  "Traceroute-like" Behavior: The PathTrack Method  . . . .   9
       4.3.1.  New RELOAD Request: PathTrack . . . . . . . . . . . .  10
     4.4.  Error Code Extensions . . . . . . . . . . . . . . . . . .  12
   5.  Diagnostic Data Structures  . . . . . . . . . . . . . . . . .  13
     5.1.  DiagnosticsRequest Data Structure . . . . . . . . . . . .  13
     5.2.  DiagnosticsResponse Data Structure  . . . . . . . . . . .  15
     5.3.  dMFlags and Diagnostic Kind ID Types  . . . . . . . . . .  16
   6.  Message Processing  . . . . . . . . . . . . . . . . . . . . .  19
     6.1.  Message Creation and Transmission . . . . . . . . . . . .  19
     6.2.  Message Processing: Intermediate Peers  . . . . . . . . .  20
     6.3.  Message Response Creation . . . . . . . . . . . . . . . .  21
     6.4.  Interpreting Results  . . . . . . . . . . . . . . . . . .  22
   7.  Authorization through Overlay Configuration . . . . . . . . .  23
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  23
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  24
     9.1.  Diagnostics Flag  . . . . . . . . . . . . . . . . . . . .  24
     9.2.  Diagnostic Kind ID  . . . . . . . . . . . . . . . . . . .  25
     9.3.  Message Codes . . . . . . . . . . . . . . . . . . . . . .  26
     9.4.  Error Code  . . . . . . . . . . . . . . . . . . . . . . .  26
     9.5.  Message Extension . . . . . . . . . . . . . . . . . . . .  26
     9.6.  XML Name Space Registration . . . . . . . . . . . . . . .  27
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  27
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  27
     10.2.  Informative References . . . . . . . . . . . . . . . . .  28
   Appendix A.  Examples . . . . . . . . . . . . . . . . . . . . . .  29
     A.1.  Example 1 . . . . . . . . . . . . . . . . . . . . . . . .  29
     A.2.  Example 2 . . . . . . . . . . . . . . . . . . . . . . . .  29
     A.3.  Example 3 . . . . . . . . . . . . . . . . . . . . . . . .  29
   Appendix B.  Problems with Generating Multiple Responses on Path   29
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  30
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  30

1. Introduction

In the last few years, overlay networks have rapidly evolved and emerged as a promising platform for deployment of new applications and services in the Internet. One of the reasons overlay networks are seen as an excellent platform for large-scale distributed systems is their resilience in the presence of failures. This resilience has three aspects: data replication, routing recovery, and static resilience. Routing recovery algorithms are used to repopulate the routing table with live nodes when failures are detected. Static resilience measures the extent to which an overlay can route around failures even before the recovery algorithm repairs the routing table. Both routing recovery and static resilience rely on accurate and timely detection of failures.

There are a number of situations in which some nodes in a Peer-to- Peer (P2P) overlay may malfunction or behave badly. For example, these nodes may be disabled, congested, or may be misrouting messages. The impact of these malfunctions on the overlay network may be a degradation of quality of service provided collectively by the peers in the overlay network or an interruption of the overlay services. It is desirable to identify malfunctioning or badly behaving peers through diagnostic tools and exclude or reject them from the P2P system. Node failures may also be caused by failures of underlying layers. For example, recovery from an incorrect overlay topology may be slow when the speed at which IP routing recovers after link failures is very slow. Moreover, if a backbone link fails and the failover is slow, the network may be partitioned, leading to partitions of overlay topologies and inconsistent routing results between different partitioned components.

Some keep-alive algorithms based on periodic probe and acknowledge mechanisms enable accurate and timely detection of failures of one node's neighbors [Overlay-Failure-Detection], but these algorithms by themselves can only detect the disabled neighbors using the periodic method. This may not be sufficient for the service provider operating the overlay network.

A P2P overlay diagnostic framework supporting periodic and on-demand methods for detecting node failures and network failures is desirable. This document describes a general P2P overlay diagnostic extension to the base protocol RELOAD [RFC6940] and is intended as a complement to keep-alive algorithms in the P2P overlay itself. Readers are advised to consult [P2PSIP-CONCEPTS] for further background on the problem domain.

2. Terminology

This document uses the concepts defined in RELOAD [RFC6940]. In addition, the following terms are used in the document:

overlay hop:

One overlay hop is one portion of path between the initiator node and the destination peer in a RELOAD overlay. Each time packets are passed to the next node in the RELOAD overlay, one overlay hop occurs.

underlay hop:

An underlay hop is one portion of the path between source and destination in the IP layer. Each time packets are passed to the next IP-layer device, an underlay hop occurs.

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].

3. Diagnostic Scenarios

P2P systems are self-organizing, and ideally the setup and configuration of individual P2P nodes requires no network management in the traditional sense. However, users of an overlay as well as P2P service providers may contemplate usage scenarios where some monitoring and diagnostics are required. We present a simple connectivity test and some useful diagnostic information that may be used in such diagnostics.

The common usage scenarios for P2P diagnostics can be broadly categorized in three classes:

a. Automatic diagnostics built into the P2P overlay routing: protocol. Nodes perform periodic checks of known neighbors and remove those nodes from the routing tables that fail to respond to connectivity checks [Handling_Churn_in_a_DHT]. Unresponsive nodes may only be temporarily disabled, for example, due to a local cryptographic processing overload, disk processing overload, or link overload. It is therefore useful to repeat the connectivity checks to see nodes have recovered and can be again placed in the routing tables. This process is known as 'failed node recovery' and can be optimized as described in the paper "Handling Churn in a DHT" [Handling_Churn_in_a_DHT].

b. Diagnostics used by a particular node to follow up on an: individual user complaint or failure. For example, a technical support staff member may use a desktop sharing application (with the permission of the user) to remotely determine the health of, and possible problems with, the malfunctioning node. Part of the remote diagnostics may consist of simple connectivity tests with other nodes in the P2P overlay and retrieval of statistics from nodes in the overlay. The simple connectivity tests are not dependent on the type of P2P overlay. Note that other tests may be required as well, including checking the health and performance of the user's computer or mobile device and checking the bandwidth of the link connecting the user to the Internet.

c. P2P system-wide diagnostics used to check the overall health of: the P2P overlay network. These include checking the consumption of network bandwidth, checking for the presence of problem links, and checking for abusive or malicious nodes. This is not a trivial problem and has been studied in detail for content and streaming P2P overlays [Diagnostic_Framework] and has not been addressed in earlier documents. While this is a difficult problem, a great deal of information that can help in diagnosing these problems can be obtained by obtaining basic diagnostic information for peers and the network. This document provides a framework for obtaining this information.

4. Data Collection Mechanisms

4.1. Overview of Operations

The diagnostic mechanisms described in this document are primarily intended to detect and locate failures or monitor performance in P2P overlay networks. It provides mechanisms to detect and locate malfunctioning or badly behaving nodes including disabled nodes, congested nodes, and misrouting peers. It provides a mechanism to detect direct connectivity or connectivity to a specified node, a mechanism to detect the availability of specified resource records, and a mechanism to discover P2P overlay topology and the underlay topology failures.

The RELOAD diagnostics extensions define two mechanisms to collect data. The first is an extension to the RELOAD Ping mechanism that allows diagnostic data to be queried from a node as well as to diagnose the path to that node. The second is a new method, PathTrack, for collecting diagnostic information iteratively. Payloads for these mechanisms allowing diagnostic data to be collected and represented are presented, and additional error codes are introduced. Essentially, this document reuses the RELOAD specification [RFC6940] and extends it to introduce the new diagnostics methods. The extensions strictly follow how RELOAD specifies message routing, transport, NAT traversal, and other RELOAD protocol features.

This document primarily describes how to detect and locate failures including disabled nodes, congested nodes, misrouting behaviors, and underlying network faults in P2P overlay networks through a simple and efficient mechanism. This mechanism is modeled after the ping/ traceroute paradigm: ping [RFC792] is used for connectivity checks, and traceroute is used for hop-by-hop fault localization as well as path tracing. This document specifies a "ping-like" mode (by extending the RELOAD Ping method to gather diagnostics) and a "traceroute-like" mode (by defining the new PathTrack method) for diagnosing P2P overlay networks.

One way these tools can be used is to detect the connectivity to the specified node or the availability of the specified resource record through the extended Ping operation. Once the overlay network receives some alarms about overlay service degradation or interruption, a Ping is sent. If the Ping fails, one can then send a PathTrack to determine where the fault lies.

The diagnostic information can only be provided to authorized nodes. Some diagnostic information can be provided to all the participants in the P2P overlay, and some other diagnostic information can only be provided to the nodes authorized by the local or overlay policy. The authorization depends on the type of the diagnostic information and the administrative considerations and is application specific.

This document considers the general administrative scenario based on diagnostic Kind, where a whole overlay can authorize a certain kind of diagnostic information to a small list of particular nodes (e.g., administrative nodes). That means if a node gets the authorization to access a diagnostic Kind, it can access that information from all nodes in the overlay network. It leaves the scenario where a particular node authorizes its diagnostic information to a particular list of nodes out of scope. This could be achieved by extension of this document if there is a requirement in the near future. The default policy or access rule for a type of diagnostic information is "deny" unless specified in the diagnostics extension document. As the RELOAD protocol already requires that each message carries the message signature of the sender, the receiver of the diagnostics requests can use the signature to identify the sender. It can then use the overlay configuration file with this signature to determine which types of diagnostic information that node is authorized for.

In the remainder of this section we define mechanisms for collecting data, as well as the specific protocol extensions (message extensions, new methods, and error codes) required to collect this information. In Section 5 we discuss the format of the data collected, and in Section 6 we discuss detailed message processing.

It is important to note that the mechanisms described in this document do not guarantee that the information collected is in fact related to the previous failures. However, using the information from previous traversed nodes, the user (or management system) may be able to infer the problem. Symmetric routing can be achieved by using the Via List [RFC6940] (or an alternate DHT routing algorithm), but the response path is not guaranteed to be the same.

4.2. "Ping-like" Behavior: Extending Ping

To provide "ping-like" behavior, the RELOAD Ping method is extended to collect diagnostic data along the path. The request message is forwarded by the intermediate peers along the path and then terminated by the responsible peer. After optional local diagnostics, the responsible peer returns a response message. If an error is found when routing, an error response is sent to the initiator node by the intermediate peer.

The message flow of a Ping message (with diagnostic extensions) is as follows:

    Peer A              Peer B               Peer C             Peer D
    
      |                    |                    |                    |
      |(1). PingReq        |                    |                    |
      |------------------->|(2). PingReq        |                    |
      |                    |------------------->|(3). PingReq        |
      |                    |                    |------------------->|
      |                    |                    |                    |
      |                    |                    |<-------------------|
      |                    |<-------------------|(4). PingAns        |
      |<-------------------|(5). PingAns        |                    |
      |(6). PingAns        |                    |                    |
      |                    |                    |                    |

Figure 1: Ping Diagnostic Message Flow

4.2.1. RELOAD Request Extension: Ping

To extend the Ping request for use in diagnostics, a new extension of RELOAD is defined. The structure for a MessageExtension in RELOAD is defined as:

            struct {
              MessageExtensionType  type;
              Boolean               critical;
              opaque                extension_contents<0..2^32-1>;
            } MessageExtension;

For the Ping request extension, we define a new MessageExtensionType, extension 0x2 named "Diagnostic_Ping", as specified in Table 4. The extension contents consists of a DiagnosticsRequest structure, defined in Section 5.1. This extension MAY be used for new requests of the Ping method and MUST NOT be included in requests using any other method.

This extension is not critical. If a peer does not support the extension, they will simply ignore the diagnostic portion of the message and will treat the message as if it were a normal ping. Senders MUST accept a response that lacks diagnostic information and SHOULD NOT resend the message expecting a reply. Receivers who receive a method other than Ping including this extension MUST ignore the extension.

4.3. "Traceroute-like" Behavior: The PathTrack Method

We define a simple PathTrack method for retrieving diagnostic information iteratively.

The operation of this request is shown below in Figure 2. The initiator node A asks its neighbor B which is the next hop peer to the destination ID, and B returns a message with the next hop peer C information, along with optional diagnostic information for B to the initiator node. Then the initiator node A asks the next hop peer C (direct response routing [RFC7263] or via symmetric routing) to return next hop peer D information and diagnostic information of C. Unless a failure prevents the message from being forwarded, this step can be repeated until the request reaches responsible peer D for the destination ID and retrieves the diagnostic information of peer D.

The message flow of a PathTrack message (with diagnostic extensions) is as follows:

   Peer-A              Peer-B               Peer-C             Peer-D
   
     |                    |                    |                    |
     |(1).PathTrackReq    |                    |                    |
     |------------------->|                    |                    |
     |(2).PathTrackAns    |                    |                    |
     |<-------------------|                    |                    |
     |                    |(3).PathTrackReq    |                    |
     |--------------------|------------------->|                    |
     |                    |(4).PathTrackAns    |                    |
     |<-------------------|--------------------|                    |
     |                    |                    |(5).PathTrackReq    |
     |--------------------|--------------------|------------------->|
     |                    |                    |(6).PathTrackAns    |
     |<-------------------|--------------------|--------------------|
     |                    |                    |                    |

Figure 2: PathTrack Diagnostic Message Flow

There have been proposals that RouteQuery and a series of Fetch requests can be used to replace the PathTrack mechanism; however, in the presence of high rates of churn, such an operation would not, strictly speaking, provide identical results, as the path may change between RouteQuery and Fetch operations. While obviously the path could change between steps of PathTrack as well, with a single message rather than two messages for query and fetch, less inconsistency is likely, and thus the use of a single message is preferred.

Given that in a typical diagnostic scenario the peer sending the PathTrack request desires to obtain information about the current path to the destination, in the event that successive calls to PathTrack return different paths, the results should be discarded and the request resent, ensuring that the second request traverses the appropriate path.

4.3.1. New RELOAD Request: PathTrack

This document defines a new RELOAD method, PathTrack, to retrieve the diagnostic information from the intermediate peers along the routing path. At each step of the PathTrack request, the responsible peer responds to the initiator node with requested status information. Status information can include a peer's congestion state, processing power, available bandwidth, the number of entries in its neighbor table, uptime, identity, network address information, and next hop peer information.

A PathTrack request specifies which diagnostic information is requested using a DiagnosticsRequest data structure, which is defined and discussed in detail in Section 5.1. Base information is requested by setting the appropriate flags in the data structure in the request. If all flags are clear (no bits are set), then the PathTrack request is only used for requesting the next hop information. In this case, the iterative mode of PathTrack is degraded to a RouteQuery method that is only used for checking the liveness of the peers along the routing path. The PathTrack request can be routed using direct response routing or other routing methods chosen by the initiator node.

A response to a successful PathTrackReq is a PathTrackAns message. The PathTrackAns contains general diagnostic information in the payload, returned using a DiagnosticResponse data structure. This data structure is defined and discussed in detail in Section 5.2. The information returned is determined based on the information requested in the flags in the corresponding request.

4.3.1.1. PathTrack Request

The structure of the PathTrack request is as follows:

                           struct{
                               Destination destination;
                               DiagnosticsRequest request;
                           }PathTrackReq;

The fields of the PathTrackReq are as follows:

   destination:  The destination that the initiator node is interested
      in.  This may be any valid destination object, including a NodeID,
      opaque ids, or ResourceID.  One example should be noted that, for
      debugging purposes, the initiator will use the destination ID as
      it was used when failure happened.
   
   request:  A DiagnosticsRequest, as discussed in Section 5.1.

4.3.1.2. PathTrack Response

The structure of the PathTrack response is as follows:

struct{

                                  Destination next_hop;
                                  DiagnosticsResponse response;
                              }PathTrackAns;

The fields of the PathTrackAns are as follows:

   next_hop:  The information of the next hop node from the responding
      intermediate peer to the destination.  If the responding peer is
      the responsible peer for the destination ID, then the next_hop
      node ID equals the responding node ID, and after receiving a
      PathTrackAns where the next_hop node ID equals the responding node
      ID, the initiator MUST stop the iterative process.
   
   response:  A DiagnosticsResponse, as discussed in Section 5.2.

4.4. Error Code Extensions

This document extends the error response method defined in the RELOAD specification to support error cases resulting from diagnostic queries. When an error is encountered in RELOAD, the Message Code 0xffff is returned. The ErrorResponse structure includes an error code. We define new error codes to report possible error conditions detected while performing diagnostics:

      Code Value     Error Code Name
         0x15        Error_Underlay_Destination_Unreachable
         0x16        Error_Underlay_Time_Exceeded
         0x17        Error_Message_Expired
         0x18        Error_Upstream_Misrouting
         0x19        Error_Loop_Detected
         0x1a        Error_TTL_Hops_Exceeded

The error code is returned by the upstream node before the failure node. The upstream node uses the normal ping to detect the failure type and return it to the initiator node, which will help the user (initiator node) to understand where the failure happened and what kind of error happened, as the failure may happen at the same location and for the same reason when sending the normal message and the diagnostics message.

As defined in RELOAD, additional information may be stored (in an implementation-specific way) in the optional error_info byte string. While the specifics are obviously left to the implementation, as an example, in the case of 0x15, the error_field could be used to provide additional information as to why the underlay destination is unreachable (net unreachable, host unreachable, fragmentation needed, etc.).

5. Diagnostic Data Structures

Both the extended Ping method and PathTrack method use the following common diagnostics data structures to collect data. Two common structures are defined: DiagnosticsRequest for requesting data and DiagnosticsResponse for returning the information.

5.1. DiagnosticsRequest Data Structure

The DiagnosticsRequest data structure is used to request diagnostic information and has the following form:

          enum{ (2^16-1) } DiagnosticKindId;
          
          struct{
              DiagnosticKindId kind;
              opaque  diagnostic_extension_contents<0..2^32-1>;
          }DiagnosticExtension;

struct{

              uint64 expiration;
              uint64 timestamp_initiated;
              uint64 dMFlags;
              uint32 ext_length;
              DiagnosticExtension diagnostic_extensions_list<0..2^32-1>;
           }DiagnosticsRequest;

The fields in the DiagnosticsRequest are as follows:

   expiration:  The time when the request will expire represented as the
   
      number of milliseconds elapsed since midnight Jan 1, 1970 UTC (not
      counting leap seconds).  This will have the same values for
      seconds as standard UNIX time or POSIX time.  More information can
      be found at "Unix time" in Wikipedia [UnixTime].  This value MUST
      have a value between 1 and 600 seconds in the future.  This value
      is used to prevent replay attacks.
   
   timestamp_initiated:  The time when the diagnostics request was
      initiated, represented as the number of milliseconds elapsed since
      midnight Jan 1, 1970 UTC (not counting leap seconds).  This will
      have the same values for seconds as standard UNIX time or POSIX
      time.
   
   dMFlags:  A mandatory field that is an unsigned 64-bit integer
      indicating which base diagnostic information the request initiator
      node is interested in.  The initiator sets different bits to
      retrieve different kinds of diagnostic information.  If dMFlags is
      set to zero, then no base diagnostic information is conveyed in
      the PathTrack response.  If dMFlags is set to all "1"s, then all
      base diagnostic information values are requested.  A request may
      set any number of the flags to request the corresponding
      diagnostic information.

Note this memo specifies the initial set of flags; the flags can be extended. The dMflags indicate general diagnostic information. The mapping between the bits in the dMFlags and the diagnostic Kind ID presented is as described in Section 9.1.

   ext_length:  The length of the extended diagnostic request
      information in bytes.  If the value is greater than or equal to 1,
      then some extended diagnostic information is being requested on
      the assumption this information will be included in the response
      if the recipient understands the extended request and is willing
      to provide it.  The specific diagnostic information requested is
      defined in the diagnostic_extensions_list below.  A value of zero
      indicates no extended diagnostic information is being requested.
      The value of ext_length MUST NOT be negative.  Note that it is not
      the length of the entire DiagnosticsRequest data structure, but of
      the data making up the diagnostic_extensions_list.
   
   diagnostic_extensions_list:  Consists of one or more
      DiagnosticExtension structures (see below) documenting additional
      diagnostic information being requested.  Each DiagnosticExtension
      consists of the following fields:
   
      kind:  A numerical code indicating the type of extension
         diagnostic information (see Section 9.2).  Note that kinds
         0xf000 - 0xfffe are reserved for overlay specific diagnostics
         and may be used without IANA registration for local diagnostic
         information.  Kinds from 0x0000 to 0x003f MUST NOT be indicated
         in the diagnostic_extensions_list in the message request, as
         they may be represented using the dMFlags in a much simpler
         (and more space efficient) way.
   
      diagnostic_extension_contents:  The opaque data containing the
         request for this particular extension.  This data is extension
         dependent.

5.2. DiagnosticsResponse Data Structure

The DiagnosticsResponse data structure is used to return the diagnostic information and has the following form:

               enum { (2^16-1) } DiagnosticKindId;
               struct{
                   DiagnosticKindId kind;
                   opaque diagnostic_info_contents<0..2^16-1>;
               }DiagnosticInfo;
               
               struct{
                   uint64 expiration;
                   uint64 timestamp_initiated;
                   uint64 timestamp_received;
                   uint8 hop_counter;
                   uint32 ext_length;
                   DiagnosticInfo diagnostic_info_list<0..2^32-1>;
               }DiagnosticsResponse;

The fields in the DiagnosticsResponse are as follows:

   expiration:  The time when the response will expire represented as
   
      the number of milliseconds elapsed since midnight Jan 1, 1970 UTC
      (not counting leap seconds).  This will have the same values for
      seconds as standard UNIX time or POSIX time.  This value MUST have
      a value between 1 and 600 seconds in the future.
   
   timestamp_initiated:  This value is copied from the diagnostics
      request message.  The benefit of containing such a value in the
      response message is that the initiator node does not have to
      maintain the state.
   
   timestamp_received:  The time when the diagnostic request was
      received represented as the number of milliseconds elapsed since
      midnight Jan 1, 1970 UTC (not counting leap seconds).  This will
      have the same values for seconds as standard UNIX time or POSIX
      time.
   
   hop_counter:  This field only appears in diagnostic responses.  It
      MUST be exactly copied from the TTL field of the forwarding header
      in the received request.  This information is sent back to the
      request initiator, allowing it to compute the number of hops that
      the message traversed in the overlay.
   
   ext_length:  The length of the returned DiagnosticInfo information in
      bytes.  If the value is greater than or equal to 1, then some
      extended diagnostic information (as specified in the
      DiagnosticsRequest) was available and is being returned.  In that
      case, this value indicates the length of the returned information.
      A value of zero indicates no extended diagnostic information is
      included either because none was requested or the request could
      not be accommodated.  The value of ext_length MUST NOT be
      negative.  Note that it is not the length of the entire
      DiagnosticsRequest data structure but of the data making up the
      diagnostic_info_list.
   
   diagnostic_info_list:  consists of one or more DiagnosticInfo
      structures containing the requested diagnostic_info_contents.  The
      fields in the DiagnosticInfo structure are as follows:
   
      kind:  A numeric code indicating the type of information being
         returned.  For base data requested using the dMFlags, this code
         corresponds to the dMFlag set and is described in Section 5.1.
         For diagnostic extensions, this code will be identical to the
         value of the DiagnosticKindId set in the "kind" field of the
         DiagnosticExtension of the request.  See Section 9.2.
   
      diagnostic_info_contents:  Data containing the value for the
         diagnostic information being reported.  Various kinds of
         diagnostic information can be retrieved.  Please refer to
         Section 5.3 for details of the diagnostic Kind ID for the base
         diagnostic information that may be reported.

5.3. dMFlags and Diagnostic Kind ID Types

The dMFlags field described above is a 64-bit field that allows initiator nodes to identify up to 62 items of base information to request in a request message (the first and last flags being reserved). The dMFlags also reserves all "0"s, which means nothing is requested, and all "1"s, which means everything is requested. But at the same time, the first and last bits cannot be used for other purposes, and they MUST be set to 0 when other particular diagnostic Kind IDs are requested. When the requested base information is returned in the response, the value of the diagnostic Kind ID will correspond to the numeric field marked in the dMFlags in the request. The values for the dMFlags are defined in Section 9.1 and the diagnostic Kind IDs are defined in Section 9.2. The information contained for each value is described in this section. Access to each kind of diagnostic information MUST NOT be allowed unless compliant to the rules defined in Section 7.

   STATUS_INFO (8 bits):  A single-value element containing an unsigned
   
      byte representing whether or not the node is in congestion status.
      An example usage of STATUS_INFO is for congestion-aware routing.
      In this scenario, each peer has to update its congestion status
      periodically.  An intermediate peer in the Distributed Hash
      Table (DHT) network will choose its next hop according to both the
      DHT routing algorithm and the status information.  This is done to
      avoid increasing load on congested peers.  The rightmost 4 bits
      are used and other bits MUST be cleared to "0"s for future use.

There are 16 levels of congestion status, with 0x00 representing zero load and 0x0f representing congestion. This document does not provide a specific method for congestion and leaves this decision to each overlay implementation. One possible option for an overlay implementation would be to take node's CPU/memory/ bandwidth usage percentage in the past 600 seconds and normalize the highest value to the range from 0x00 to 0x0f. An overlay implementation can also decide to not use all the 16 values from 0x00 to 0x0f. A future document may define an objective measure or specific algorithm for this.

   ROUTING_TABLE_SIZE (32 bits):  A single-value element containing an
      unsigned 32-bit integer representing the number of peers in the
      peer's routing table.  The administrator of the overlay may be
      interested in statistics of this value for reasons such as routing
      efficiency.
   
   PROCESS_POWER (64 bits):  A single-value element containing an
      unsigned 64-bit integer specifying the processing power of the
      node with MIPS as the unit.  Fractional values are rounded up.
   
   UPSTREAM_BANDWIDTH (64 bits):  A single-value element containing an
      unsigned 64-bit integer specifying the upstream network bandwidth
      (provisioned or maximum, not available) of the node with units of
      kbit/s.  Fractional values are rounded up.  For multihomed hosts,
      this should be the link used to send the response.
   
   DOWNSTREAM_BANDWIDTH (64 bits):  A single-value element containing an
      unsigned 64-bit integer specifying the downstream network
      bandwidth (provisioned or maximum, not available) of the node with
      kbit/s as the unit.  Fractional values are rounded up.  For
      multihomed hosts, this should be the link the request was received
      from.
   
   SOFTWARE_VERSION:  A single-value element containing a US-ASCII
      string that identifies the manufacture, model, operating system
      information, and the version of the software.  Given that there
      are a very large number of peers in some networks, and no peer is
      likely to know all other peer's software, this information may be
      very useful to help determine if the cause of certain groups of
      misbehaving peers is related to specific software versions.  While
      the format is peer defined, a suggested format is as follows:
      "ApplicationProductToken (Platform; OS-or-CPU) VendorProductToken
      (VendorComment)", for example, "MyReloadApp/1.0 (Unix; Linux
      x86_64) libreload-java/0.7.0 (Stonyfish Inc.)".  The string is a
      C-style string and MUST be terminated by "\0"."\0" MUST NOT be
      included in the string itself to prevent confusion with the
      delimiter.
   
   MACHINE_UPTIME (64 bits):  A single-value element containing an
      unsigned 64-bit integer specifying the time the node's underlying
      system has been up (in seconds).
   
   APP_UPTIME (64 bits):  A single-value element containing an unsigned
      64-bit integer specifying the time the P2P application has been up
      (in seconds).
   
   MEMORY_FOOTPRINT (64 bits):  A single-value element containing an
      unsigned 64-bit integer representing the memory footprint of the
      peer program in kilobytes (1024 bytes).  Fractional values are
      rounded up.
   
   DATASIZE_STORED (64 bits):  An unsigned 64-bit integer representing
      the number of bytes of data being stored by this node.
   
   INSTANCES_STORED:  An array element containing the number of
      instances of each kind stored.  The array is indexed by Kind-ID.
      Each entry is an unsigned 64-bit integer.
   
   MESSAGES_SENT_RCVD:  An array element containing the number of
      messages sent and received.  The array is indexed by method code.
      Each entry in the array is a pair of unsigned 64-bit integers
      (packed end to end) representing sent and received.
   
   EWMA_BYTES_SENT (32 bits):  A single-value element containing an
      unsigned 32-bit integer representing an exponential weighted
      average of bytes sent per second by this peer:

sent = alpha x sent_present + (1 - alpha) x sent_last

where sent_present represents the bytes sent per second since the last calculation and sent_last represents the last calculation of bytes sent per second. A suitable value for alpha is 0.8 (or another value as determined by the implementation). This value is calculated every five seconds (or another time period as determined by the implementation). The value for the very first time period should simply be the average of bytes sent in that time period.

   EWMA_BYTES_RCVD (32 bits):  A single-value element containing an
      unsigned 32-bit integer representing an exponential weighted
      average of bytes received per second by this peer:

rcvd = alpha x rcvd_present + (1 - alpha) x rcvd_last

where rcvd_present represents the bytes received per second since the last calculation and rcvd_last represents the last calculation of bytes received per second. A suitable value for alpha is 0.8 (or another value as determined by the implementation). This value is calculated every five seconds (or another time period as determined by the implementation). The value for the very first time period should simply be the average of bytes received in that time period.

   UNDERLAY_HOP (8 bits):  Indicates the IP-layer hops from the
      intermediate peer, which receives the diagnostics message to the
      next-hop peer for this message.  (Note: RELOAD does not require
      the intermediate peers to look into the message body.  So, here we
      use PathTrack to gather underlay hops for diagnostics purpose).
   
   BATTERY_STATUS (8 bits):  The leftmost bit is used to indicate
      whether this peer is using a battery or not.  If this bit is clear
      (set to "0"), then the peer is using a battery for power.  The
      other 7 bits are to be determined by specific applications.

6. Message Processing

6.1. Message Creation and Transmission

When constructing either a Ping message with diagnostic extensions or a PathTrack message, the sender first creates and populates a DiagnosticsRequest data structure. The timestamp_initiated field is set to the current time, and the expiration field is constructed based on this time. The sender includes the dMFlags field in the structure, setting any number (including all) of the flags to request particular diagnostic information. The sender MAY leave all the bits unset, thereby requesting no particular diagnostic information.

The sender MAY also include diagnostic extensions in the DiagnosticsRequest data structure to request additional information.

If the sender includes any extensions, it MUST calculate the length of these extensions and set the ext_length field to this value. If no extensions are included, the sender MUST set ext_length to zero.

The format of the DiagnosticRequest data structure and its fields MUST follow the restrictions defined in Section 5.1.

When constructing a Ping message with diagnostic extensions, the sender MUST create a MessageExtension structure as defined in RELOAD [RFC6940], setting the value of type to 0x2 and the value of critical to FALSE. The value of extension_contents MUST be a DiagnosticsRequest structure as defined above. The message MAY be directed to a particular NodeID or ResourceID but MUST NOT be sent to the broadcast NodeID.

When constructing a PathTrack message, the sender MUST set the message_code for the RELOAD MessageContents structure to path_track_req 0x27. The request field of the PathTrackReq MUST be set to the DiagnosticsRequest data structure defined above. The destination field MUST be set to the desired destination, which MAY be either a NodeID or ResourceID but SHOULD NOT be the broadcast NodeID.

6.2. Message Processing: Intermediate Peers

When a request arrives at a peer, if the peer's responsible ID space does not cover the destination ID of the request, then the peer MUST continue processing this request according to the overlay specified routing mode from RELOAD protocol.

In P2P overlay, error responses to a message can be generated by either an intermediate peer or the responsible peer. When a request is received at a peer, the peer may find connectivity failures or malfunctioning peers through the predefined rules of the overlay network, e.g., by analyzing the Via List or underlay error messages. In this case, the intermediate peer returns an error response to the initiator node, reporting any malfunction node information available in the error message payload. All error responses generated MUST contain the appropriate error code.

Each intermediate peer receiving a Ping message with extensions (and that understands the extension) or receiving a PathTrack request / response MUST check the expiration value (Unix time format) to determine if the message is expired. If the message expired, the intermediate peer MUST generate a response with error code 0x17 "Error_Message_Expired", return the response to the initiator node, and discard the message.

The intermediate peer MUST return an error response with the error code 0x15 "Error_Underlay_Destination_Unreachable" when it receives an ICMP message with "Destination Unreachable" information after forwarding the received request to the destination peer.

The intermediate peer MUST return an error response with the error code 0x16 "Error_Underlay_Time_Exceeded" when it receives an ICMP message with "Time Exceeded" information after forwarding the received request.

The peer MUST return an error response with error code 0x18 "Error_Upstream_Misrouting" when it finds its upstream peer disobeys the routing rules defined in the overlay. The immediate upstream peer information MUST also be conveyed to the initiator node.

The peer MUST return an error response with error code 0x19 "Error_Loop_Detected" when it finds a loop through the analysis of the Via List.

The peer MUST return an error response with error code 0x1a "Error_TTL_Hops_Exceeded" when it finds that the TTL field value is no more than 0 when forwarding.

6.3. Message Response Creation

When a diagnostic request message arrives at a peer, it is responsible for the destination ID specified in the forwarding header, and assuming it understands the extension (in the case of Ping) or the new request type PathTrack, it MUST follow the specifications defined in RELOAD to form the response header, and perform the following operations:

When constructing a PathTrack response, the sender MUST set the message_code for the RELOAD MessageContents structure to path_track_ans 0x28.

The receiver MUST check the expiration value (Unix time format) in the DiagnosticsRequest to determine if the message is expired. If the message is expired, the peer MUST generate a response with the error code 0x17 "Error_Message_Expired", return the response to the initiator node, and discard the message.

If the message is not expired, the receiver MUST construct a DiagnosticsResponse structure as follows: 1) the TTL value from the forwarding header is copied to the hop_counter field of the DiagnosticsResponse structure (note that the default value for TTL at the beginning represents 100 hops unless the overlay configuration has overridden the value), and 2) the receiver generates a Unix time format timestamp for the current time of day and places it in the timestamp_received field and constructs a new expiration time and places it in the expiration field of the DiagnosticsResponse.

The destination peer MUST check if the initiator node has the authority to request specific types of diagnostic information, and if appropriate, append the diagnostic information requested in the dMFlags and diagnostic_extensions (if any) using the diagnostic_info_list field to the DiagnosticsResponse structure. If any information is returned, the receiver MUST calculate the length of the response and set ext_length appropriately. If no diagnostic information is returned, ext_length MUST be set to zero.

The format of the DiagnosticResponse data structure and its fields MUST follow the restrictions defined in Section 5.2.

In the event of an error, an error response containing the error code followed by the description (if they exist) MUST be created and sent to the sender. If the initiator node asks for diagnostic information that they are not authorized to query, the receiving peer MUST return an error response with the error code 2 "Error_Forbidden".

6.4. Interpreting Results

The initiator node, as well as the responding peer, may compute the overlay One-Way-Delay time through the value in timestamp_received and the timestamp_initiated field. However, for a single hop measurement, the traditional measurement methods (IP-layer ping) MUST be used instead of the overlay layer diagnostics methods.

The P2P overlay network using the diagnostics methods specified in this document MUST enforce time synchronization with a central time server. The Network Time Protocol [RFC5905] can usually maintain time to within tens of milliseconds over the public Internet and can achieve better than one millisecond accuracy in local area networks under ideal conditions. However, this document does not specify the choice for time resolution and synchronization, leaving it to the implementation.

The initiator node receiving the Ping response may check the hop_counter field and compute the overlay hops to the destination peer for the statistics of connectivity quality from the perspective of overlay hops.

7. Authorization through Overlay Configuration

Different level of access control can be made for different users/ nodes. For example, diagnostic information A can be accessed by nodes 1 and 2, but diagnostic information B can only be accessed by node 2.

The overlay configuration file MUST contain the following XML elements for authorizing a node to access the relative diagnostic Kinds.

   diagnostic-kind:  This has the attribute "kind" with the hexadecimal
      number indicating the diagnostic Kind ID.  This attribute has the
      same value with Section 9.2 and at least one subelement "access-
      node".
   
   access-node:  This element contains one hexadecimal number indicating
      a NodeID, and the node with this NodeID is allowed to access the
      diagnostic "kind" under the same diagnostic-kind element.

8. Security Considerations

The authorization for diagnostic information must be designed with care to prevent it becoming a method to retrieve information for both attacks. It should also be noted that attackers can use diagnostics to analyze overlay information to attack certain key peers. For example, diagnostic information might be used to fingerprint a peer where the peer will lose its anonymity characteristics, but anonymity might be very important for some P2P overlay networks, and defenses against such fingerprinting are probably very hard. As such, networks where anonymity is of very high importance may find implementation of diagnostics problematic or even undesirable, despite the many advantages it offers. As this document is a RELOAD extension, it follows RELOAD message header and routing specifications. The common security considerations described in the base document [RFC6940] are also applicable to this document. Overlays may define their own requirements on who can collect/share diagnostic information.

9. IANA Considerations

9.1. Diagnostics Flag

IANA has created a "RELOAD Diagnostics Flag" registry under protocol RELOAD. Entries in this registry are 1-bit flags contained in a 64-bit integer dMFlags denoting diagnostic information to be retrieved as described in Section 4.3.1. New entries SHALL be defined via Standards Action as per [RFC5226]. The initial contents of this registry are:

     +-------------------------+----------------------------+----------+
     |  Diagnostic Information |Diagnostic Flag in dMFlags  | Reference|
     |-------------------------+----------------------------+----------|
     |Reserved All 0s value    | 0x 0000 0000 0000 0000     | RFC 7851 |
     |Reserved First Bit       | 0x 0000 0000 0000 0001     | RFC 7851 |
     |STATUS_INFO              | 0x 0000 0000 0000 0002     | RFC 7851 |
     |ROUTING_TABLE_SIZE       | 0x 0000 0000 0000 0004     | RFC 7851 |
     |PROCESS_POWER            | 0x 0000 0000 0000 0008     | RFC 7851 |
     |UPSTREAM_BANDWIDTH       | 0x 0000 0000 0000 0010     | RFC 7851 |
     |DOWNSTREAM_ BANDWIDTH    | 0x 0000 0000 0000 0020     | RFC 7851 |
     |SOFTWARE_VERSION         | 0x 0000 0000 0000 0040     | RFC 7851 |
     |MACHINE_UPTIME           | 0x 0000 0000 0000 0080     | RFC 7851 |
     |APP_UPTIME               | 0x 0000 0000 0000 0100     | RFC 7851 |
     |MEMORY_FOOTPRINT         | 0x 0000 0000 0000 0200     | RFC 7851 |
     |DATASIZE_STORED          | 0x 0000 0000 0000 0400     | RFC 7851 |
     |INSTANCES_STORED         | 0x 0000 0000 0000 0800     | RFC 7851 |
     |MESSAGES_SENT_RCVD       | 0x 0000 0000 0000 1000     | RFC 7851 |
     |EWMA_BYTES_SENT          | 0x 0000 0000 0000 2000     | RFC 7851 |
     |EWMA_BYTES_RCVD          | 0x 0000 0000 0000 4000     | RFC 7851 |
     |UNDERLAY_HOP             | 0x 0000 0000 0000 8000     | RFC 7851 |
     |BATTERY_STATUS           | 0x 0000 0000 0001 0000     | RFC 7851 |
     |Reserved Last Bit        | 0x 8000 0000 0000 0000     | RFC 7851 |
     |Reserved All 1s value    | 0x ffff ffff ffff ffff     | RFC 7851 |
     +-------------------------+----------------------------+----------+

9.2. Diagnostic Kind ID

IANA has created a "RELOAD Diagnostic Kind ID" registry under protocol RELOAD. Entries in this registry are 16-bit integers denoting diagnostics extension data kinds carried in the diagnostic request and response messages, as described in Sections and 5.1 and 5.2. Code points from 0x0001 to 0x003e are asked to be assigned together with flags within the "RELOAD Diagnostics Flag" registry. The registration procedure for the "RELOAD Diagnostic Kind ID" registry is Standards Action as defined in RFC 5226.

         +----------------------+---------------+---------------+
         | Diagnostic Kind      |      Code     | Specification |
         +----------------------+---------------+---------------+
         | Reserved             |     0x0000    |    RFC 7851   |
         | STATUS_INFO          |     0x0001    |    RFC 7851   |
         | ROUTING_TABLE_SIZE   |     0x0002    |    RFC 7851   |
         | PROCESS_POWER        |     0x0003    |    RFC 7851   |
         | UPSTREAM_BANDWIDTH   |     0x0004    |    RFC 7851   |
         | DOWNSTREAM_BANDWIDTH |     0x0005    |    RFC 7851   |
         | SOFTWARE_VERSION     |     0x0006    |    RFC 7851   |
         | MACHINE_UPTIME       |     0x0007    |    RFC 7851   |
         | APP_UPTIME           |     0x0008    |    RFC 7851   |
         | MEMORY_FOOTPRINT     |     0x0009    |    RFC 7851   |
         | DATASIZE_STORED      |     0x000a    |    RFC 7851   |
         | INSTANCES_STORED     |     0x000b    |    RFC 7851   |
         | MESSAGES_SENT_RCVD   |     0x000c    |    RFC 7851   |
         | EWMA_BYTES_SENT      |     0x000d    |    RFC 7851   |
         | EWMA_BYTES_RCVD      |     0x000e    |    RFC 7851   |
         | UNDERLAY_HOP         |     0x000f    |    RFC 7851   |
         | BATTERY_STATUS       |     0x0010    |    RFC 7851   |
         | Unassigned           | 0x0011-0x003e |    RFC 7851   |
         | local use (Reserved) | 0xf000-0xfffe |    RFC 7851   |
         | Reserved             |     0xffff    |    RFC 7851   |
         +----------------------+---------------+---------------+

Table 1: Diagnostic Kind

9.3. Message Codes

This document introduces two new types of messages and their responses, so the following additions have been made to the "RELOAD Message Codes" registry defined in RELOAD [RFC6940].

               +-------------------+------------+----------+
               | Message Code Name | Code Value |   RFC    |
               +-------------------+------------+----------+
               |   path_track_req  |    0x27    | RFC 7851 |
               |   path_track_ans  |    0x28    | RFC 7851 |
               +-------------------+------------+----------+

Table 2: Extensions to RELOAD Message Codes

9.4. Error Code

This document introduces the following new error codes, which have been added to the "RELOAD Error Codes" registry.

    +----------------------------------------+------------+-----------+
    | Error Code Name                        | Code Value | Reference |
    +----------------------------------------+------------+-----------+
    | Error_Underlay_Destination_Unreachable |    0x15    |  RFC 7851 |
    | Error_Underlay_Time_Exceeded           |    0x16    |  RFC 7851 |
    | Error_Message_Expired                  |    0x17    |  RFC 7851 |
    | Error_Upstream_Misrouting              |    0x18    |  RFC 7851 |
    | Error_Loop_Detected                    |    0x19    |  RFC 7851 |
    | Error_TTL_Hops_Exceeded                |    0x1A    |  RFC 7851 |
    +----------------------------------------+------------+-----------+

Table 3: RELOAD Error Codes

9.5. Message Extension

This document introduces the following new RELOAD extension code:

                  +-----------------+------+-----------+
                  |  Extension Name | Code | Reference |
                  +-----------------+------+-----------+
                  | Diagnostic_Ping | 0x2  |  RFC 7851 |
                  +-----------------+------+-----------+

Table 4: New RELOAD Extension Code

9.6. XML Name Space Registration

This document registers a URI for the config-diagnostics XML namespace in the IETF XML registry defined in [RFC3688]. All the elements defined in this document belong to this namespace.

   URI: urn:ietf:params:xml:ns:p2p:config-diagnostics
   Registrant Contact: The IESG.
   XML: N/A; the requested URIs are XML namespaces

The overlay configuration file MUST contain the following XML language declaring P2P diagnostics as a mandatory extension to RELOAD.

   <mandatory-extension>
                 urn:ietf:params:xml:ns:p2p:config-diagnostics
   </mandatory-extension>

10. References

10.1. Normative References

   [RFC792]   Postel, J., "Internet Control Message Protocol", STD 5,
              RFC 792, DOI 10.17487/RFC0792, September 1981,
              <http://www.rfc-editor.org/info/rfc792>.
   
   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.
   
   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              DOI 10.17487/RFC3688, January 2004,
              <http://www.rfc-editor.org/info/rfc3688>.
   
   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              DOI 10.17487/RFC5226, May 2008,
              <http://www.rfc-editor.org/info/rfc5226>.
   
   [RFC5905]  Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
              "Network Time Protocol Version 4: Protocol and Algorithms
              Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010,
              <http://www.rfc-editor.org/info/rfc5905>.
   
   [RFC6940]  Jennings, C., Lowekamp, B., Ed., Rescorla, E., Baset, S.,
              and H. Schulzrinne, "REsource LOcation And Discovery
              (RELOAD) Base Protocol", RFC 6940, DOI 10.17487/RFC6940,
              January 2014, <http://www.rfc-editor.org/info/rfc6940>.
   
   [RFC7263]  Zong, N., Jiang, X., Even, R., and Y. Zhang, "An Extension
              to the REsource LOcation And Discovery (RELOAD) Protocol
              to Support Direct Response Routing", RFC 7263,
              DOI 10.17487/RFC7263, June 2014,
              <http://www.rfc-editor.org/info/rfc7263>.

10.2. Informative References

   [UnixTime] Wikipedia, "Unix time", April 2016,
              <https://en.wikipedia.org/w/
              index.php?title=Unix_time&oldid=715503178>.

[P2PSIP-CONCEPTS]

              Bryan, D., Matthews, P., Shim, E., Willis, D., and S.
              Dawkins, "Concepts and Terminology for Peer to Peer SIP",
              Work in Progress, draft-ietf-p2psip-concepts-09, April
              2016.

[Overlay-Failure-Detection]

              Zhuang, S., Geels, D., Stoica, I., and R. Katz, "On
              failure detection algorithms in overlay networks", In
              Proceedings of the IEEE INFOCOM 2005, pp. 2112-2123,
              DOI 10.1109/INFCOM.2005.1498487, March 2005.

[Handling_Churn_in_a_DHT]

Rhea, S., Geels, D., Roscoe, T., and J. Kubiatowicz,

"Handling Churn in a DHT", In Proceedings of the

USENIX Annual Technical Conference, June 2004.

[Diagnostic_Framework]

              Jin, X., Xiong, Y., Zhang, Q., and S. Chan, "A Diagnostic
              Framework for Peer-to-peer Streaming", IEEE ICME 2006,
              July 2006.

Appendix A. Examples

Below, we sketch how these metrics can be used.

A.1. Example 1

A peer may set EWMA_BYTES_SENT and EWMA_BYTES_RCVD flags in the PathTrackReq to its direct neighbors. A peer can use EWMA_BYTES_SENT and EWMA_BYTES_RCVD of another peer to infer whether it is acting as a media relay. It may then choose not to forward any requests for media relay to this peer. Similarly, among the various candidates for filling up a routing table, a peer may prefer a peer with a large UPTIME value, small RTT, and small LAST_CONTACT value.

A.2. Example 2

A peer may set the STATUS_INFO Flag in the PathTrackReq to a remote destination peer. The overlay has its own threshold definition for congestion. The peer can obtain knowledge of all the status information of the intermediate peers along the path, then it can choose other paths to that node for the subsequent requests.

A.3. Example 3

A peer may use Ping to evaluate the average overlay hops to other peers by sending PingReq to a set of random resource or node IDs in the overlay. A peer may adjust its timeout value according to the change of average overlay hops.

Appendix B. Problems with Generating Multiple Responses on Path

An earlier draft version of this document considered an approach where a response was generated by each intermediate peer as the message traversed the overlay. This approach was discarded. One reason this approach was discarded was that it could provide a DoS mechanism, whereby an attacker could send an arbitrary message claiming to be from a spoofed "sender" the real sender wished to attack. As a result of sending this one message, many messages would be generated and sent back to the spoofed "sender" -- one from each intermediate peer on the message path. While authentication mechanisms could reduce some risk of this attack, it still resulted in a fundamental break from the request-response nature of the RELOAD protocol, as multiple responses are generated to a single request. Although one request with responses from all the peers in the route will be more efficient, it was determined to be too great a security risk and a deviation from the RELOAD architecture.

Acknowledgments

We would like to thank Zheng Hewen for the contribution of the initial draft version of this document. We would also like to thank Bruce Lowekamp, Salman Baset, Henning Schulzrinne, Jiang Haifeng, and Marc Petit-Huguenin for the email discussion and their valued comments, and special thanks to Henry Sinnreich for contributing to the usage scenarios text. We would like to thank the authors of the RELOAD protocol for transferring text about diagnostics to this document.

Authors' Addresses

Haibin Song
Huawei

   Email: haibin.song@huawei.com

Jiang Xingfeng
Huawei

Email:

          jiangxingfeng@huawei.com

Roni Even
Huawei
14 David Hamelech
Tel Aviv 64953
Israel

   Email: ron.even.tlv@gmail.com

David A. Bryan
ethernot.org
Cedar Park, Texas
United States

Email:

          dbryan@ethernot.org

Yi Sun
ICT

   Email: sunyi@ict.ac.cn